Tuesday, March 29, 2011

THE human gut contains a diverse community of bacteria which colonize the small intestine in the days following birth and vastly outnumber our own cells. These intestinal microflora constitute a virtual organ within an organ and influence many bodily functions. Among other things, they aid in the uptake and metabolism of nutrients, modulate the inflammatory response to infection, and protect the gut from other, harmful micro-organisms. A new study by researchers at McMaster University in Hamilton, Ontario now suggests that gut bacteria may also influence behaviour and cognitive processes such as memory by exerting an effect on gene activity during brain development.

Jane Foster and her colleagues compared the performance of germ-free mice, which lack gut bacteria, with normal animals on the elevated plus maze, which is used to test anxiety-like behaviours. This consists of a plus-shaped apparatus with two open and two closed arms, with an open roof and raised up off the floor. Ordinarily, mice will avoid open spaces to minimize the risk of being seen by predators, and spend far more time in the closed than in the open arms when placed in the elevated plus maze.

This is exactly what the researchers found when they placed the normal mice into the apparatus. The animals spent far more time in the closed arms of the maze and rarely ventured into the open ones. The germ-free mice, on the other hand, behaved quite differently - they entered the open arms more often, and continued to explore them throughout the duration of the test, spending significantly more time there than in the closed arms.

The researchers then examined the animals' brains, and found that these differences in behaviour were accompanied by alterations in the expression levels of several genes in the germ-free mice. Brain-derived neurotrophic factor (BDNF) was significantly up-regulated, and the 5HT1A serotonin receptor sub-type down-regulated, in the dentate gyrus of the hippocampus. The gene encoding the NR2B subunit of the NMDA receptor was also down-regulated in the amygdala.

All three genes have previously been implicated in emotion and anxiety-like behaviours.

It seems that the mice were not bred to have some other condition that would cause them to lack intestinal bacteria by gene inheritance. That thoughts and emotions might truly be the result of the variety of living organisms living within us is intriguing.

Evidently we should eat more yougurt.

I'd bet the Huffington Post has some woo on this, but I think it's important to strike them until they pay bloggers. I won't even link to them.